Since primary cells of the type having a zinc anode mostly use a strong alkaline electrolyte (e.g. a concentrated aqueous solution of KOH saturated with ZnO), they must be sealed over their casings so as to avoid leakage of the alkaline electrolyte. This, however, results unfavorably in enclosure of hydrogen gas generated due to corrosion of the zinc anode. Thus if the sealing is perfect, the pressure of the hydrogen gas evolved may increase during the storage of the cell and can sometimes lead to the critical point at which the cell may explode.
To preclude such unfavorable phenomena, there have been reported many improvements on the cell construction in an attempt to minimize the effect of hydrogen gas pressure. However, these improvements are, in most cases, insufficient to achieve prevention of a possible explosion of the cell.
The most useful or effective technique to prevent such an alteration inside the cell is one in which an amalgamated zinc powder is used as an anode active material so as to achieve inhibition of corrosion by way of increasing hydrogen overvoltage of zinc.
Heretofore, there have been employed two types of process for manufacturing such an amalgamated zinc powder, that is, a process in which a molten zinc added with mercury is atomized to form particles, and a process in which zinc powder is placed in a liquid and subject to contact with mercury.
The amalgamated zinc powder as produced by these conventional processes, however, contains 5 to 10% wt% of mercury by necessity to prevent corrosion of zinc, and is therefore harmful to human being or other living things and can cause environmental pollution.